The field of art to which this invention pertains is synthetic resins containing hydrophilic groups, said resins being soluble or dispersible in water when salted.
Industrial coating processes utilizing aqueous dispersions or solutions of organic resinous film forming compositions continue to grow in importance. The aqueous coating compositions are used in various applications, such as spray coating, flow coating and electrodeposition coating processes.
Resinous compositions which contain carboxylic acid groups capable of being salted with a base have been found to be particularly useful in the manufacture of aqueous coating compositions. Examples of such resinous compositions can be found in U.S. Pat. No. 3,230,162 wherein the reaction of maleinized fatty acids with polyepoxide resins is described. The acid groups react with the epoxide groups and/or the anhydride groups react with the hydroxyl groups of the polyepoxide resins forming ester groups. The unreacted acid or anhydride groups (after hydrolysis) can then be salted with a base and the resinous composition can be dissolved or dispersed in water. Similar compositions are described in U.S. Pat. No. 3,308,077. Related compositions are set forth in U.S. Pat. No. 3,862,914 wherein polycarboxylic acid monoanhydrides, e.g., trimellitic anhydride, are reacted with polyepoxide resins. Although such compositions have found wide utility in the coating industry, they have a disadvantage in that under some conditions the coating compositions made from the polycarboxylic resins are unstable due to the presence of the ester group. The ester groups are subject to hydrolysis and saponification in aqueous systems in the presence of a base.
Another class of resins which have found utility in aqueous compositions are polyamine resins. Such resins when salted with an acid also are soluble or dispersible in water. Examples of polyamine resins are described in U.S. Pat. No. 4,031,050 and 4,017,438, wherein polyepoxide resins are adducted with polyamines. The adducts which contain unreacted primary, secondary, or tertiary amine groups are salted with acids to form water soluble or dispersible systems. The use of epoxy-amine adducts in aqueous paint compositions avoids the problems of ester group instability. However, the use of acids as solubilizing agents presents corrosion problems in storing, handling, applying and baking the coating compositions.